T lymphocytes from rats infected with Nippostrongylus brasiliensis form a soluble factor which selectively potentiates the IgE response (IgE-potentiating factor). If one takes mesenteric lymph node cells 8 days after infection and incubates the lymphocytes with IgE, another soluble factor which selectively suppresses the IgE response, is formed. Both IgE potentiating factor and IgE-suppressive factor have affinity for IgE. In this fiscal year, we shall study the source of IgE-suppressive factor and look for immunological methods to increase the population. Chemical difference between IgE-potentiating factor and IgE-suppressive factor will be investigated.